Answer
$y=-\pi\ cos(x)$
Work Step by Step
1. Based on the given graph, we can initially identify that it resembles a graph of negative cosine.
2. We can determine the amplitude $|A|=\pi$, period $p=2\pi$, passing $(0,-\pi)$.
3. Write a model as $y=-\pi\ cos(\omega x)$
4. We have $\frac{2\pi}{\omega}=2\pi$, thus $\omega=1$
5. The equation is $y=-\pi\ cos(x)$
